DE 10 2009 047 861 discloses a high-pressure discharge lamp having a discharge vessel, in which a starting aid is used at the end of the discharge vessel.
Free electrons need to be generated in the discharge vessel for starting high-pressure discharge lamps. Until now, this has been provided by radioactive krypton-85 in the filling gas. Gas discharge lamps without radioactivity in the filling gas can start much more reliably when starting aids are used, for example a UV enhancer.
When the lamp geometry does not permit an additional starting aid, sometimes a discharge in an outer bulb can be used as a UV light source; see US 2003034738, WO2008007284. By suitably selecting the gas in the outer bulb, the outer bulb discharge usually has a lower starting voltage than the lamp. However, these voltages are still higher than the starting voltages of lamps filled with radioactive krypton-85.
Other known starting aids require more or less high starting voltages depending on the embodiment; see EP-A 2306492.